Actual story
This is kind of funny, so I'll pass it on. It was an actual case I learned in law school when I was taking a family law course.
There was a teacher in Pennsylvania (I think it was in the late seventies or early eighties), who began to have an affair with one of his seriously underage students.
The mother tried to keep them apart, but nothing worked, so charges were about to be filed, and then (as everybody knows) kiss that teacher goodbye.
But the teacher had a lawyer who not only read the law, but understood it. It seems that Pennsylvania during its frontier days had a relatively relaxed standard about the age a girl would have to be to enter into a common law marriage, and the marriage did not have to be approved or sanctioned by the girl's parents.
As a result, the teacher had the girl come over,and in front of witnesses, they staged a common law marriage ceremony.
When the prosecutor tried to bring charhes, the judge threw them out, essentially stating that the law was n the books, and that was that. Although the law has since been changed, the age necessary for a common law marriage in Pennsylania at that time was 7!